Abstract: Towoard the bearing capacity design issue for the stirring shaft， the torque， deformation and the stress situations were studied based on computational fluid dynamic simulation and fluid-structure interaction analysis by working with various viscosity materials， for the multi-layer stirring and fermentation machine for high viscosity material. The strength-safe viscosity limits and range are calculated according to the torque force of the stirring device， as well as the torque of stirring device under different filling height was analyzed. The results indicated that the on-paddle torque in the first layer is the largest， and the largest deformation happens in the finally the sixth layer. Besides the maximum stress occurs in the shaft segment between the short shaft and the first layer stirring paddle. The safe viscosity limit is 205Pa·s. The height variation of the filling material has little effect to the torque in the stirring device and the optimum heitht range is 100~150mm from the material surface to the top of stirring tank.

Key words: fluid-solid interaction, stirring device, finite element simulation, viscosity